1. Field of the Invention
The present application relates generally to the field of seismic data acquisition and processing, and particularly to using surface consistent decomposition for seismic data acquisition and processing quality control.
2. Background
Geophysical prospecting has been used extensively in the search for underground resources such as oil, gas, and minerals. Common techniques used for exploration include seismic, gravity, magnetic, and electrical methods. Seismic is historically the most widely used and can be subcategorized into seismic reflection and seismic refraction methods. With the seismic reflection method, the structure of subsurface formations is mapped by measuring the times required for a seismic wave, generated in the earth by a near-surface explosion, mechanical impact, vibration, or air gun, for example, to return to the surface after reflection from interfaces between formations having different physical properties. The reflections are recorded by detecting instruments responsive to ground motion or pressure waves. With reflection methods, one can locate and map, for example, such features as anticlines, faults, salt domes, and reefs.
The recorded data generally are processed using computers prior to being interpreted. The basic objective of seismic processing is to convert the information recorded in the field into a form that best facilitates geological interpretation. The field data are transformed into corrected record sections. One object of the processing is to eliminate or reduce noise. Another is to present the reflections with the greatest possible resolution.
Digital filtering is one commonly used processing method. One type of digital filtering is known as deconvolution. Because the reflected signal is effectively filtered or convolved by the earth as it passes from the source to the receiver, an inverse filter is produced that ideally cancels the effect of the earth's filtering. That is, the deconvolution operation converts the waveform of a reflection modified by the filtering of the earth into a simple pulse representing the reflection waveform before the filtering took place.
Seismic reflection data have historically been deconvolved using single-channel spiking deconvolution. That technique, however, is based on the false assumption that the reflectivity series are “white”. That is, the deconvolution filter is designed to produce a reflection signal that is a spike, meaning all frequency components of the reflection signal's frequency spectrum have equal amplitudes. A spike would provide the highest resolution possible. However, absorption of higher frequencies by the earth broadens the source signal so that it is no longer white. Single-channel spiking deconvolution is also sensitive to random noise because any deconvolution program that raises the high frequency response could magnify existing noise in the record.
Surface consistent deconvolution is a multichannel deconvolution using a geometric mean and gathers of common shots, common receivers, common midpoints, and common offsets. This process provides a deconvolution operator for every shot and receiver gather, corresponding respectively to the source function and the receiver impulse response, as well as an estimate of the reflectivity functions at every common midpoint (CMP) location.